1. Field of the Invention
This invention relates to a process for the conversion of a feedstock comprising aliphatic hydrocarbons to aromatics in the presence of a zeolite catalyst prepared without a directing agent, as hereinafter defined.
2. Background Information
Zeolites have been used in the past in the preparation of catalysts for the production of aromatic hydrocarbons from aliphatic hydrocarbons by passing the aliphatic hydrocarbon over the catalyst at an elevated temperature in the liquid or vapor phase. Zeolites of various types have been suggested for the preparation of such catalysts, e.g., ZSM-type zeolites containing any of various cations such as hydrogen, ammonium, or metallic cations, e.g., gallium, or containing any of various metal oxides impregnated on its surface, e.g., a gallium oxide. However, when using these zeolite catalysts, any means which can be employed to improve the yield of desirable aromatics such as benzene, toluene, and the xylenes is generally considered desirable.
3. Information Disclosure Statement
The following information is disclosed in accordance with the terms of 37 CFR 1.56, 1.97 and 1.98.
Cattanach, U.S. Pat. Nos. 3,756,942 and 3,760,024, discloses the preparation of aromatic compounds from aliphatic compounds using as catalyst a ZSM-type zeolite in which at least some of the original cations have been replaced by hydrogen, ammonium or metallic cations, or impregnated with a metallic component as described previously. The patentee also contemplates a thermal treatment in air or a steam treatment at a temperature up to 1500.degree. F. (816.6.degree. C.).
Davies et al., U.S. Pat. No. 4,180,689, teaches processes for the production of aromatics by contacting a C.sub.3 -C.sub.12 hydrocarbon feedstock with a catalyst in which gallium is supported on an aluminosilicate, e.g. ZSM-5. After addition of the gallium, the catalyst is activated at a temperature of between 400.degree. and 650.degree. C.
Telford, U.S. Pat. No. 4,304,686, teaches the aromatization of aliphatic hydrocarbons utilizing as catalyst a zeolite having a silica/alumina molar ratio of 10:1 to 500:1 in which at least some of the cations have been exchanged for gallium ions. The zeolite is calcined at a temperature of at least 300.degree. C., suitably between 300.degree. and 800.degree. C., before being treated to effect the gallium exchange.
Chester et al., U.S. Pat. No. 4,350,835, teach a catalytic process for converting a feedstock comprising a high percentage of ethane to aromatics employing as a catalyst a zeolite, e.g., ZSM-5, with a silica/alumina ratio of at least 12 and having incorporated therein a minor amount of gallium. The zeolite is calcined at 540.degree. C. before the incorporation of the gallium.
Telford et al., U.S. Pat. No. 4,487,853 discloses the conversion of hydrocarbon feedstocks to aromatics using a catalyst subjected during its preparation to a steam treatment followed by loading with a Group IIIb metal, especially gallium. The catalyst may also be calcined under dry conditions at or about 550.degree. C. one or more times in the course of its preparation.
Plank et al., U.S. Patent Nos. 4,175,114; 4,199,556; and 4,341,748, teach the preparation of zeolites, e.g., ZSM-5, without employing any organic cations, but utilizing instead seeds of the desired zeolite in the formulating mixture which seeds themselves were formed in the presence of organic ions or from other seeds formed in the presence of organic ions, etc., and/or an aliphatic alcohol containing 2 to 5 carbon atoms. The patentees show the use of their zeolites as catalysts for "M-forming," i.e., the alkylation of benzene with n-heptane.
European Patent Application Publication No. 50,021 teaches a process for producing aromatic hydrocarbons by contacting a feedstock containing at least 70% weight of C.sub.2 hydrocarbons with a catalyst comprising an aluminosilicate, e.g., ZSM-5, with a silica/alumina molar ratio of at least 5:1, and in which either gallium is deposited thereon, or cations have been exchanged with gallium ions. After the incorporation of the gallium, the catalyst is activated at a temperature of between 400.degree. C. and 650.degree. C.
In each of the foregoing references, the disclosed zeolite is formed in the presence of an organic and/or inorganic directing agent as hereinafter defined.
European Patent Application Publication No. 106,552 discloses the preparation of zeolites similar to ZSM-5 by crystallizing a homogeneous phase compound of a granular amorphous aluminosilicate in water or in an aqueous solution of an alkali metal hydroxide and/or an alkali metal silicate. The zeolites are prepared "without using organic and inorganic mineralizers," which mineralizers appear to be substantially equivalent to what applicants refer to as organic or inorganic directing agents or templates. The patent publication points out that the zeolite, after being ion-exchanged with appropriate cations, can be used as a catalyst in the form of a crystal aggregate or after fine pulverization, but does not mention any specific reaction which can be catalyzed.
European Patent Application Publication No. 119,023 discloses the improvement of the catalytic activity of a zeolite for the aromatization of paraffins by steam treating the zeolite and then loading it with a Group IIIB metal, especially gallium. The zeolite is prepared in the presence of an organic directing agent.
Pending parent application Ser. No. 14,147, filed Feb. 12, 1987, teaches the synthesis of various zeolites, e.g., ZSM-5, by crystallizing a reaction mixture comprising a precipitated amorphous silica or aluminosilicate having a particle size of 1 to 500 microns. No organic "template" or "directing agent" is utilized in the preparation and the disclosure also contemplates preparation in which no inorganic directing agents, e.g., zeolite seeds, are employed. The application discloses the use of the zeolite as a catalyst in the aromatization of paraffins and olefins. That portion of the disclosure of Ser. No. 14,147 which deals with the preparation and use of zeolites contemplated by this invention, e.g., aluminosilicate zeolites having a Constraint Index in the range of about 1 to 12, and prepared by crystallizing a composition free of any organic or inorganic directing agents, e.g., organic amines or ammonium salts of such organic amines, or zeolite seeds, is incorporated herein by reference.